1. Field of the Invention:
This invention is directed to a method and apparatus for remote control of audio speakers. More particularly, the invention is directed to placing microprocessor intelligence in remote speakers for individual control of speakers in a network system from a central control point in the network. The invention is particularly useful in public address systems.
2. Description of Prior Art:
Public address systems have been configured traditionally with multiple speakers cabled together, and driven with a common signal or cabled together as multiple networks or zones with a common signal per zone. The common signal originates from one or more sources of audio signal selected for transmission to all speakers or to all speakers in a zone.
It is desirable to provide more flexibility in a speaker system network by being able to use separate audio signals at each speaker in the network. For example, an operator at a central point may wish to transmit a message to only selected speakers in a network, or in multiple networks or zones, rather to all speakers in a network or zone. It is also desirable to provide separate volume control at each speaker, and to selectively mix more than one audio signal at selected speakers in the network system. For example, a public address system might have music broadcast to all speakers and then mix with that music an announcement which would go to selected speakers in the system.
The advent of digital audio signals has facilitated the distribution of audio signals-from source to speakers. For example, U.S. Pat. No. 4,922,536 entitled "Digital Audio Transmission For Use In Studio, Stage Or Field Applications," uses FDM/TDM (Frequency Division and Time Division Multiplexing) to digitally transmit audio signals from multiple microphones to a control booth, and to digitally transmit audio signals from the control booth to speakers. At each end of the digital transmission, the digital signals are converted to analog signals for processing. The control booth provides the control for all the speakers. In another example, use of a microprocessor in a computing system to control routing of audio signals on a computer bus are shown in U.S. Pat. No. 4,862,159 entitled "Centralized System For Selecting And Reproducing Perceptible Programs." In both of these audio systems, the speakers are dumb devices; there is no digital audio processing at the speakers themselves.
Speakers with limited intelligence are described in U.S. Pat. No. 4,621,374 entitled "Circuit Arrangement For Processing, Transmitting, and Acoustically Reproducing Digitized Audio-Frequency Signals." This patent teaches RF transmission of digital audio signals and audio control signals to individual speakers. The audio control signals are volume, tone, balance. These control signals are processed in a signal processor before the audio signal is converted to an analog signal for the speaker. Audio signals may be transmitted to a particular speaker by using a transmission carrier frequency assigned to that speaker.
Another example of microprocessor control of a speaker is described in U.S. Pat. No. 4,550,400 entitled "Remote Digital Volume Control System." This patent uses remote speaker units having a control console at the speaker unit. The audio signals are broadcast as TDM digital audio data to all speakers. Each source of audio data is placed in a time slot on the TDM bus. A control console at the remote speaker can select an audio source by selecting a time slot, and by controlling volume to the selected audio signal. Multiple audio signals may be mixed in an analog manner at the speaker by leakage properties between the audio filter/line drivers.
Accordingly, microprocessors have been placed at remote speaker units, the microprocessors have performed only simple tasks such as volume or tone control.